PROJECT SUMMARY/ABSTRACT The transcription factors of the NF-kB family are central regulators of a wide variety of biological processes. This includes events as fundamental as embryonic development and cellular survival as well as the intricate responses of the innate and adaptive immune system. What has remained elusive are the mechanisms that allow this limited set of five proteins to orchestrate the radically different transcriptional programs which are required for these disparate cellular functions. Understanding the details of NF-kB-dependent transcription, however, is of paramount importance for efforts to achieve targeted therapeutic intervention in cases of pathological NF-kB activation, such as sepsis, rheumatoid arthritis and cancer. One of the factors that fine-tune NF-kB activation is the inhibitor of NF-kB, isoform b (IkB-b), which has been shown to serve an intriguing dual role as a conventional inhibitor, and atypical co-activator, of NF-kB- dependent transcription. In unstimulated cells, IkB-b sequesters NF-kB dimers in the cytoplasm and thus prevents transcriptional activation, whereas upon stimulation a nuclear form of IkB-b enhances transcription of a subset of NF-kB-dependent genes. Consequently, IkB-b-deficient macrophages produce starkly reduced levels of the cytokine TNF-a following exposure to an activating stimulus, whereas levels of the cytokine IL-6 are largely unaffected. The goal of this project is to comprehensively understand the role of IkB-b as a selective co-activator of NF-kB activation. This will be accomplished by rigorously characterizing the mechanism that underlies IkB-b function on a biochemical and molecular level. Furthermore, the full extent of IkB-b co-activator function and its effect on global transcription will be probed using cutting-edge genomics techniques, including RNA-seq and ChIP- seq. These data sets will then be integrated to create a holistic model of IkB-b function. Finally, the true physiological relevance of IkB-b will be determined in vivo with mouse models of acute and chronic inflammation, as well as bacterial infection.